Infrared observations of circumstellar ammonia in OH/IR supergiants Ammonia has been detected in the circumstellar envelopes of VY CanisMajoris, VX Sagittarii, and IRC +10420 by means of several absorptionlines in the nu-2 vibration-rotation band near 950 kaysers. The lineprofiles are well resolved (0.2 km/sec resolution) and show the gasbeing accelerated to terminal expansion velocities near 30 km/sec. Theobservations reveal a method for determining the position of the centralstar on VLBI maps of OH maser emission to an accuracy of approximately0.2 arcsec. A firm lower limit of 2 x 10 to the 15th/sq cm is obtainedfor the NH3 column density in VY Canis Majoris.